The present invention relates to enclosed electronics assemblies and associated methods of manufacture, and more particularly to explosion-proof field devices with removable covers and methods of manufacturing the same.
Field devices, which can include industrial process transmitters, controllers, etc., are used in industrial process facilities in a variety of settings. For example, field devices can include a sensor to sense pressure, temperature, vibration, flow, or nearly any other parameter associated with an industrial process, and/or can include an actuator or other device that manages, controls, or otherwise interacts with an industrial process. Many industrial process facilities are located in corrosive environments, or may be subject to a risk of fire, explosion, or vibration, and therefore field devices must generally be constructed to be explosion-proof and otherwise able to suitably withstand operating environment conditions. The field device can communicate—wirelessly or using a hard-wired connection—with a control room, other device, etc. to help provide industrial process management. Typically, field devices are installed at desired locations and are configured by an operator at the installation location using a programming device. However, such programming devices can be costly, and must be transported to the installation location for use by the operator. Yet it is desired to be able to configure field devices without having to remove transmitter covers, because covers may be difficult to remove and then reinstall and cover removal undesirably exposes interior regions of the transmitters to the environment. It is therefore desired to provide a local operator interface suitable for use with a field device.
Field devices typically utilize a threaded cover that is removably secured to a transmitter housing to provide an explosion-proof enclosure. However, the torque exerted when engaging (or disengaging) the cover with the transmitter housing as well as vibrations or shocks encountered during operation could possibly disrupt, damage or even destroy sensitive circuitry if the cover physically contacts that circuitry or associated structures (e.g., a display glass carrying the LOI circuitry). For such reasons, a conventional threaded cover is problematic in providing a local operator interface (LOI) for a field device with LOI components located near the cover.
FIG. 1 is an exploded perspective view of a prior art pipe union assembly 20 (available from Rosemount, Inc., Chanhassen, Minn., as Part No. 00079-0288-0001) that meets the explosion-proof requirements of International Electrotechnical Commission (IEC) standard 60079-1 (2007). The assembly 20 includes a first fitting 22, a second fitting 24, and a collar 26. The first and second fittings 22 and 24 are generally open-ended cylindrical members used to connect adjacent pipes, conduits, etc. The first and second fittings 22 and 24 have mating serrations 28 (the serrations 28 on the first fitting are not visible in FIG. 1) that engage to form an explosion-proof flame path. The collar 26 can be positioned around the second fitting 24 against a shoulder 30 thereof and threaded onto the first fitting 22 to force the second fitting 24 into engagement with the first fitting 22. The assembly 20 allows rotation between the first and second fittings 22 and 24.